Apparatus for measuring the partial pressure of gases or vapors

ABSTRACT

An apparatus comprising a chemically sensitive sensor material, having an electrical resistance or dielectric constant which changes under the effect of the gases or vapors. According to the invention, this sensor material, which comprises either hydrophobic metal complexes, or a mixture of at least one phthalide and at least one acidic compound, serves as resistance or as dielectric material. These sensor materials change their ion mobility and/or their ionic concentration under the effect of gases or vapors, thereby changing their resistance or capacitance. The change in resistance or the change in capacitance can expediently be converted into a frequency change by a multivibrator. Thus, one obtains an especially simple and very effective sensor for gases and vapors.

This application is related to commonly assigned U.S. application Ser.No. 323,345, filed the same day, entitled "Sensor Material for Measuringthe Partial Pressure of Gases or Vapors; and Gas Sensor", the disclosureof which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an apparatus for continuously measuringthe partial pressure of gases or vapors with a chemically sensitivesensor material. The chemically sensitive sensor material has anelectrical resistance or dielectric constant that changes under theeffect of the gas or vapor.

BACKGROUND OF THE INVENTION

Generally known sensors for measuring gases and vapors are opticalfilters containing a sensor material which reversibly changes color inthe presence of a gas or vapor. This color change affects thetransmittancy of the filter under the influence of the gases or vapors.These filters contain a mixture of an alkaline, or acid, color former,also known as a colorant, and a complementary compound. Triphenylmethanecompositions, preferably crystal violet lactone, for example can beutilized as color formers ("colorants"). These filters may also comprisecolorants of the triphenylmethane system, preferably phthalein orsulphophthalein, which can be embedded in a matrix and provided with acarrier. The change in the transmittancy of the filter, under the effectof the gases or vapors, is converted into an electric signal andprocessed electronically. A filter such as generally described above isdiscussed in German Published Patent Application No. 35 06 686.

Metal complexes having ligands with hydrophobing properties aregenerally known. Examples of these metal complexes include: monodentateligands, for example dimethyl formamide; bidentate ligands; chelateligands, for example ethylenediamine and acetylacetone, podandens andmacrocylenes such as crown ethers and cryptands.

A change in electrical properties, such as a change in the dielectricconstant or the electrical conductivity of a material, can be utilizedto measure, or sense, gases or vapors, see, for example, Sensorik,Springer Publishers Heidelberg, 1986, pages 195-199. This effect can beutilized in a simple way, such as with a gas sensor in the form of acondenser, to measure the humidity of the air. In this type of sensorthe water-adsorbing dielectric material is applied to metal electrodes.The second electrode of the condenser is applied to the dielectricmaterial, in the form of two engaging finger patterns, to form acomb-like structure. A dielectric material, which changes its dielectricconstant under the effect of a gas, is superimposed over this comb-likestructure. The corresponding change in the capacitance serves as asensor signal.

The present invention provides a simple sensor system for gases orvapors, which enables the partial pressure or the concentration ofvirtually all solvents and gases to be continuously measured, even atlow temperatures.

SUMMARY OF THE INVENTION

According to the present invention, a hydrophobic metal complex, or amixture comprising at least one phthalide and at least one acidiccompound, are provided as electric resistance sensor material or asdielectric sensor material in a sensor. Under the effect of gases orvapors, these sensor materials demonstrate a change in ionicconcentration or ion mobility. A sensor system for gases or vapors withthese sensor materials can be economically designed as a small andeasily transportable, hand-operated, instrument. The sensor materials ofthe present invention also make it possible without undue expertise, toestablish the existence of gases and vapors at any location, even atroom temperature.

In a preferred embodiment the sensor system further comprises an astable multivibrator, which converts the change in resistance, or thechange of the dielectric constant, into a frequency change.

The sensor material of the present invention at least partiallycomprises macrocyclic metal complexes, preferably the ligands of thecrown ether or cryptand type. For example §-benzo [15] crown-5 or also§-benzo-cryptand, for example§-5,6-benzo-4,7,13,16,21,24-hexoaxa-1.10-diazobicyclo-(8,8,8-hexacosancan be selected as ligands. These compounds are known under thedesignation §-222_(B). The metal complexes of the present inventionpreferably comprise a polymer crown ether or cryptand, which coordinateswith a variably charged metal ion, such as a sodium ion, Na⁺ ; or apotassium ion, K⁺ ; or a magnesium ion, Mg++. Polymer structures, whichcan be used to produce stable layers, are preferred.

Macrocyclic metal complexes, with counter ions of variable nucleophiles,preferably chloride anions Cl⁻ or perchlorate anions ClO₄ ⁻ may also beutilized in the present invention.

Compounds suitable for anion or cation solvation, which can thereforestabilize positively or negatively charged particles are suitableco-substances. For example, solid or also polyfunctional alcohols,preferably pyrogallol or etherified polyethylene glycols, are suitableco-substances.

phthalides, preferably substituted phthalides, for example 3-(N-methyl1-3-indolyl 1)-6-dimethylaminophthalide are also suitable for use in thepresent invention. Also suited are 3,3-diphenylphthalides, for example3-(p-dimethylaminophenyl)-3-(p-methoxyphenyl)-6-dimethyl aminophthalideor 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, which isknown under the designation crystal violet lactone.

Preferable acidic co-substances are phenolic acids, preferably2,2-(4-hydroxyphenyl)-propane, which is sold commercially under thedesignation "Bisphenol-A", orhydroxy-(phenyl)-bis(p-hydroxyphenyl)-methane, which is soldcommercially under the designation "Benzaurin".

Suitable transparent supporting materials include glass and plastics.The sensor-active material may also be embedded in a matrix. Inorganicand organic polymer substances, such as polyvinyl chloride, silicons andcollodion, and polymers with active functional groups, which are suitedfor cation and anion solvation, are suitable matrix materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the present invention in a schematic topview.

FIG. 2 shows a side view of the embodiment shown in FIG. 1.

FIG. 3 shows an electrical schematic of a multivibrator.

FIG. 4 is a graph plotting the frequency, in kilohertz, with respect tothe concentration of ethanol for an embodiment of the present invention.

FIG. 5 is a graph plotting the frequency, in kilohertz, with respect toacetone concentration for an embodiment of the present invention.

FIG. 6 shows an immersion sensor according to the present invention.

FIG. 7 shows an optical immersion sensor according to the presentinvention.

FIG. 8 shows a portion of an optical immersion sensor according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In the embodiment of the present invention shown in FIG. 1, a gas sensor2 has two electrodes, 4 and 5 respectively, are arranged in a comb-likestructure, with engaging teeth, on a substrate, 10 with a length L ofapproximately 40 mm and a width B of approximately 8 mm shown in theside view of FIG. 2. Substrate 10 can be made of glass. Electrodes 4 and5 have large-surface ends adapted to connect electric conductors. Forthis purpose, electrodes 4 and 5 may be furnished with additional metalcoatings 6 and 7, which may be copper. An electric supply lead, 11 or12, respectively, is attached, by soldering, to each metal coating. Theband-shaped teeth of the comb-like structure of both electrodes, notshown in great detail in the figure, are arranged at a slight distance"a" from each other. The distance "a" may be between approximately 10and approximately 50 μm. The width "b" of the band-shaped teeth may bebetween approximately 100 and approximately 200 μm.

A predetermined quantity of a solution containing the sensor material isapplied dropwise onto the comb-like structure of both electrodes 4 and 5and the solvent is evaporated. Electrodes 4 and 5 have a thickness "d",shown in FIG. 2, up to about 0.5 μm. Thereby, a cohesive sensor layer isformed with a thickness "c", selected to be at least large enough toavoid an island formation. Thickness "c" therefore, preferably amountsto at least 50 nm and, in general, does not significantly exceed 2 mm.Metal coating 7, with its supply lead, 12, is also depicted in FIG. 2.The change in the capacitance, or the resistance, of the sensor layer14, in response to a gas or vapor, serves as an output signal for thegas sensor 2.

In another embodiment of the sensor system of the present invention, thechange in the resistance, or the capacitance, of the sensor layer 14 canbe converted into a frequency change. For this purpose, an a stablemultivibrator 20 as shown in FIG. 3, can be provided. Input E, of this astable multivibrator, may be connected to a circuit voltage U₁ equal to5 V. To measure the change in the capacitance of the sensor layer 14 ofthe sensor 2, the supply leads 11 and 12 of the sensor 2 are connectedto the multivibrator supply terminals designated 22 and 23. In the formof this embodiment with capacitance measurement, a ground resistor 16 isinserted between two additional terminals 24 and 25. As a result of thecapacitance change in the sensor layer 14 of the sensor 2, acorresponding frequency change in the output voltage U₂ is obtained atthe output A of the multivibrator 20. In the case of the embodiment of asensor layer 14, whereby its change in resistance serves as a signal, aground capacitor is connected between the terminals 22 and 23 of themultivibrator 20, and the sensor 2, with its supply leads 11 and 12, isconnected between the terminals 24 and 25.

In the embodiment of the sensor 2, in which resistance is measured, amacrocyclic metal complex, with good electric conductivity, can beapplied as resistance material to form a sensor layer 14. This can be acomplex comprising potassium chloride and polymer crown ether§-B[15]K-5. To measure, for example, the ethanol concentration of airwith a 50% moisture content, one obtains, a frequency, at output A ofthe multivibrator 20 according to the characteristic curve K1 of FIG. 4.In FIG. 4, the frequency "f" in KHz is plotted with respect to theethanol concentration C_(E) in 10⁻¹ %. An appropriate measuringinstrument may be calibrated according to the characteristic curve K₁.

In the embodiment of the sensor 2 in which capacitance is measuredsensor layer 14 may comprise a substitute 3,3-diphenylphthalide,##STR1## with bisphenol-A (1:4) as a co-substance, according to thefollowing description. This mixture demonstrates a relatively highresistance and serves as a dielectric in the measurement setup. Thediagram of FIG. 5 shows the frequency, in KHz of the multivibrator 20 asa function of acetone concentration C_(A) in 10⁻¹ %. K₂ of FIG. 5 showsthe characteristic frequency curve for the acetone concentration of airwith a 50% moisture content. An appropriate measuring instrument may becalibrated according to the characteristic curve K₂.

The system with the basic unit from the sensor 2, and with themultivibrator 20, can also be designed as an immersion sensor, as shownin FIG. 6. In this embodiment the sensor is provided with a chamber 26,having an inner wall at least partially comprising a gas permeablemembrane, 28, shown with a dotted line in FIG. 6.

The optical immersion sensor embodiment of the present invention, shownin FIG. 7, to prove the existence of gases and liquids in solutionsusing light guide technology, comprises a light source 32, a lightguide, serving as a supply line 34, a light guide serving as a returnline 35, and a receiver 38. The extremities of both light guides, 34 and35, can form a common optical fiber bundle, 36, whereby a reflector, 30contains the sensor layer, 14, preferably provided with a carrier, 42.The end of the optical fiber bundle 36, with the reflector 30, ispreferably provided with a casing 44, which serves as a membrane.

A light emitting diode (LED), preferably a laser, more preferably animpulse-commutate semiconductor laser, can be utilized as a light source32. The light guides 34 and 35 respectively, may comprise a bundle ofglass fibers, which are combined at the end to form a common glass fiberbundle 36. A portion of the glass fibers serve to supply the light beam,and the remaining portion serve to lead back the reflecting light.Reflector 30 preferably comprises a layer of a 3,3-diphenylphthalide,with a thickness of approximately 0.1 to 0.2 μm. Carrier 42 may comprisea plastic film, preferably a polyester film, having a thickness ofapproximately 100 μm. The casing 44 may comprise a material which allowsthe gas to be measured, or the vapor from the liquid to be measured, tobe diffused out of the measuring solution 16 to the reflector 30.Tetrafluorethylene (Teflon), for example, has this property and istherefore suitable for casing 44.

In another embodiment of the sensor, both light guide 34 and light guide35 can be arranged next to each other, as shown in FIG. 8, such that theend faces of light guides 34 and 35, lie on their ends in one plane. Aprism, provided with the sensor layer 14, serves as a reflector 30, andis attached to both end faces. The oncoming rays 48, in the light guide34, indicated by a broken line in FIG. 8, are then redirected, afterreflecting twice on the lateral surfaces, to the light guides 35. Thereflected quantity of light changes if the transmissivity, or the color,of the reflector 30 changes under the effect of the gas.

A conical reflector can also be provided, having the end faces of bothlight guides 34 and 35 attached to its base, so that they lie directlynext to each other. As with the prism, the covering of the conicalreflector is supplied with the sensor layer 14.

We claim:
 1. An apparatus for continuously measuring the partialpressure of gases or vapors with a chemically sensitive sensor material,having an electrical resistance or dielectric constant that changes inresponse to a change in the partial pressure of the gas or vapor, thesensor material comprising:a dielectric material, having an ion mobilityor ion concentration which changes in response to a change in thepartial pressure of the gas or vapor, selected from the group consistingof a metal complex having at least one hydrophobing ligand and a mixtureof at least one phthalide with at least one acidic component.
 2. Theapparatus of claim 1, further comprising an a stable multivibrator whichconverts a change in the electric resistance or the dielectric constantinto a change in frequency.
 3. The apparatus of claim 1, wherein themetal complex further comprises macrocyclic metal complexes.
 4. Theapparatus of claim 3, wherein the macrocyclic metal complex furthercomprises crown ether.
 5. The apparatus of claim 3, wherein themacrocyclic metal complex further comprises §-benzo[15]crown-5.
 6. Theapparatus of claim 3, wherein the macrocyclic metal complex furthercomprises cryptands.
 7. The apparatus of claim 6, wherein the cryptandsfurther comprises §-benzo-cryptands.
 8. The apparatus of claim 7,wherein the §-benzo-cryptands further comprise §-222_(B).
 9. Theapparatus of claim 1, further comprising variably charged metal ions.10. The apparatus of claim 9, wherein the variably charged metal ionsare selected from the group consisting of sodium ion, Na⁺ ; a potassiumions, K⁺ ; and a magnesium ions, Mg⁺⁺.
 11. The apparatus of claim 1,further comprising metal complexes with counter ions of variablenucleophiles.
 12. The apparatus of claim 11, wherein the metal complexeswith counter ions of variable nucleophiles are selected from the groupconsisting of chloride anions, Cl⁻ and perchlorate anions, ClO₄ ⁻. 13.The apparatus of claim 1, further comprising at least one proticco-substance.
 14. The apparatus of claim 13, wherein the proticco-substance further comprises pyrogallol.
 15. The apparatus of claim 1,further comprising at least one aprotic co-substance.
 16. The apparatusof claim 1, wherein the phthalide further comprises etherfiedpolyethylene glycols.
 17. The apparatus of claim 1, wherein thephthalide further comprises a substitute phthalide.
 18. The apparatus ofclaim 17, wherein the substitute phthalide further comprises3-(N-methyl-3-indolyl)-6-dimethylaminophthalide.
 19. The apparatus ofclaim 17, wherein the substitute phthalide further comprises a3,3-diphenylphthalide.
 20. The apparatus of claim 19, wherein the3,3-diphenylphthalide further comprises3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide.
 21. Theapparatus of claim 19, wherein the 3,3-diphenylphthalide furthercomprises3-(p-dimethylaminophenyl)-3-(p-methoxyphenyl)-6-dimethylaminophthalide.22. The apparatus of claim 1, wherein the acidic component furthercomprises phenolic acids.
 23. The apparatus of claim 22, wherein thephenolic acids further comprise 2,2-bis(4-hydroxyphenyl)-propane. 24.The apparatus of claim 22, wherein the phenolic acid further compriseshydroxy-(phenyl)-bis(p-hydroxyphenyl)-menthane.
 25. The apparatus ofclaim 1, wherein the sensor material is embedded in a matrix substance.26. The apparatus of claims 1, wherein the sensor material is arrangedon one carrier.
 27. The apparatus of claim 1 further comprising:achamber containing the sensor material and a gas permeable membraneforming at least one side of the chamber.